Method of treating paper pulp to obtain paper of improved water resistance



Patented June 10, 1930 I UNITED STATESIPATENT OFFICE GEORGE JAMES MANSON, OF HAWKESBURY, ONTARIO, CANADA METHOD OF TREATING PAPER PULP {1'0 OBTAIN PAPER. OF IMPROVED WATER RESISTANCE Application filed March 14, 1927. Serial No. 175,427.

This invention relates to a process of makfor example, a solution of silicate of soda and ing a water resistant paper, or one which is rendered sufliciently resistant to the ingress of moisture to serve various applications Where so-called waterproof paper or board is required, and relates particularly to paper containing a wax such as paraifin wax as the major or essentialwaterproofing agent, said paper having good strength and preferably plossessing what is known as crackle or rat- My invention comprises paper Which is waterproofed with such waxy material, preferably incorporated with the pulp, as, for example, in the beater engine, applied in the form of a dispersion or emulsion. In one form of the invention I contemplate avoiding the employment of any resinuous size such as ordinary rosin size. The latter is supposed to give stiffness and rattle to paper, while paraflin wax is supposed to render. paper limp. The rosin size is expected to give strength, while it is assumed that wax Will tend to cause weakness. In carrying out the present invention I am enabled to produce, even without the employment of any rosin size, a relatively strong paper having a desirable rattle or crackle and a stifl'ness meeting commercial requirements.

The usual rocedure in thesizing of paper pulp, with, or example, rosin size, is that of adding a rosin soap or-mixture of rosin and rosin soap to the paper pulp in the beater engine and after mixingthoroughly with the pulp to add a precipitant or coagulant; alum being the material usually employed for such purposes.

In accordance with the present invention a product is obtained from a wax such as paraffin wax which contains wax particles in so fine a form of division or in some peculiar form of dispersion, such that a precipitant is not necessarily required to secure adhesion of the particles of wax to the'cellulose fibres.

The waxy element or ingredient of the composition preferably is essentially paraflin wax and for this purpose, in some cases, scale wax or other cheap grade of paraflin wax may be employed.

Wax preferably is first incorporated with,

an emulsion produced, whereupon a quantity of a precipitant such as hydrated lime, alum, and the like, is'added to react completely with the silicate of soda. By this procedure the Wax is obtained in a dispersed form having the. property aforesaid of becoming occluded or taken up by moist fibres of wood or cellulose.

In some cases a protective colloid such as a small amount of glue, casein, and the like, may form an ingredient of the composition, being added preferably with the silicate of soda. In other cases the Wax may contain a small amount of oleic or stearic acid. In still other cases the wax may have incorporated with it a varying proportion of vegetable Waxes such as candelilla or carnauba wax or an acidic mineral wax such as montan wax or montanic acid. The incorporation of such hard waxes with the paraffin wax serves to modify its melting point and to some extent its properties of dispersion. The wax or mixture of waxes may be incorporated withthe silicate of soda by melting the former and placing in an agitator, whereupon-the solution of silicate of soda is added and the mixture thoroughly agitated for a short time. Then a precipitant, for example, a quantity of alum equivalent to the sodium silicate is added and agitation continued for an additional brief period, Whereupon the dispersed wax composition is obtained ready for use. Preferably this composition should contain from 25 to 30 per cent of waxy material and preferably, though not necessarily, such compositions should be practically neutral to ordinary tests such as that with litmus. Its pH value preferably should range from 7 to 7 .3.

Examples of such compositions are the following:

Example 1:

Parts by weight Paraflin wax 33 Silicate of soda 4-. Alum 2 Glue 1 Water 60 The silicate of soda used in the above formula is a commercial form of syrupy consistency containing about 50 per cent of water. This silicate of soda syrup was mixed with 65 per cent of the total water. The remaining 35 per cent of the total water was used to dissolve the alum. The glue was added to the diluted silicate of soda. The wax composition was prepared by first melt-ing the wax, adding the silicate of soda solution containing the glue and agitating, finally adding the alum solution with agitation. The temperature at which the composiiton is prepared is about 170 F.

E wample 93:

Parts by weight Paraffin wax 32.5

In this case, as in Example 1, the silicate of soda specified is a syrup containing about 50 per cent of water. In like manner this syrup is diluted with 65 per cent of the total water and the alum is dissolved in the 'remainder of the water employed.

The glue is dissolved in the silicate of soda solution. It is desirable to add 1 or 2 per cent of phenol, based on the amount of glue, in order to preserve the latter. The waxes are melted together and the silicate of soda solution containing the glue is added thereto with thorough agitation, the temperature be ing about 17 0 F. The alum solution is then added and agitation continued for a short time.

E sample 3:

, ass Paraflin wax 31 Montan wax 7 Silicate of soda 2.65 Alum 1.35 Water 58 The silicate of soda syrup is diluted with a part of the water and the alum is diluted with the remainder, somewhat similar to the manner set forth in Examples 1 and 2. The waxes are melted together and the silicate of soda solution is added thereto with vigorous agitation at a' working temperature of 170 F. When the incorporation is thoroughly eflected, the alum solution is introduced. A very fine wax dispersion results.

E wample 4:

Paraffin wax 37 Quick lime 1.7 Alum 4.6 Water 56.7

The quick lime is treated with about 65 per cent of the total water and the alum is dissolved in the remaining water. The wax is melted and placed in an agitator and the milk of lime is added. After stirring vigorously for about one minute the alum solution is added and agitation continued for two minutes, when the wax composition is ready for use. As in the foregoing it is recommended that the working temperature in the preparation of the wax composition be about 17 0 F.

The foregoing compositions serve to illustrate the present invention, but it should be understood that these procedures are set forth solely for illustrative purposes and that various modifications with respect to proportions, temperatures and procedure and manner of incorporation may be utilized, also that substances of an equivalent character may replace one or more of the foregoing constituents.

I prefer to dilute the wax composition (which comes from the agitator containing approximately 30 per cent of waxy material) until it contains about 5 per cent of waxy material and add it in the diluted state to the beater through a screen of about 60 mesh. I have found that this insures a better dispersion through the stock in the beater. When using waxes containing rosin soaps and free rosin it is necessary to closely control the acidity of the stock after the size is added to assure proper coagulation of the size on the fibres, this acidity having a value corresponding to pH of about 4.5. Rosin size, furthermore, should be preferably added to stock that is slightly alkaline. I have found that when the wax composition involved in the present invention is used that the acidity of the paper stock, after said composition is added, is not at all critical, and may vary from an acidity corresponding to a pH value of 4.5 to 7 without affecting the retention of the wax by the fibre. I have also found that the wax composition can be added to the pulp if the pulp is acid, that is, corresponding to a pH value of from 5 to 6.5. In this case it is not necessary to add any further precipitant such as alum. This allows of a considerable saving of alum. The stock being less acid increases the life of the various parts of the system such as pumps, piping and wires.

The following will serve as an illustration of the beneficial effect of the use of this wax composition 4 A plant engaged in the forming of pulp articles and using ordinary standard rosin' size had considerable difficulty due to the rosin adhering to the wires on the forming machines, making a product which had badly formed edges and holes. They also had trouble with their piping system and pumps on account of the acidity of the stock due to the use of the amount of alum necessary to pr cipitate the rosin size. In this plant when rosin size was discontinued and a wax com position made in the manner above set forth was employed, no trouble was experienced with the products sticking to the wires on the forming machine, and furthermore the production was increased at least 15 per cent, with the .product being uniformly much cleaner on the edges and tougher, that is, not as brittle as previously.

As the pulp was nearly neutral to litmus when the wax size was used there would not be the expected deterioration of the pipings and pumps consequent on the procedure involved in using rosin size.

I have found that using wax composition mentioned above, a retention of the wax on the fibres of from 75 per cent to 90 per cent,

depending on the nature of the stock, resulted. Moreover, any wax that-is not retained on the fibre does not adhere to the felts or wires of the paper machine or forming machines, but is carried away with the white water. Wax which does not adhere to tne pulp fibres must not adhere to the felt and to the wires, as this would prevent drainage of the pulp sheet and cause holes in the sheet, or spots on the surface of the sheet.

I have found that the addition of only 1 per cent of wax will give water resisting qualities satisfactory for the ordinary uses to which paper products are put, although for special purposes the amount of wax can be increased to 4 or 5 per cent. I have found that the addition of wax up to 5 per cent v tends to increase the strength and to improve the rattle or stiffness. This is a surpr1s1ng result as paraflin wax has been supposed to have a lubricating action on fibres and thus yield a weak limp paper. Paper containing this wax dispersion is not as susceptible to changes in atmospheric moisture, 1

and for this reason is peculiarly adapted to use in the printing trade where it is necessary to register two or more impressions. I have found that paper containing 1 to 1 per cent of wax and 1 to 2 per cent of rosin, the rosin being added as ordinary rosin size, does not lose strength when subjected to the action of a greasy material as paper does when it is only sized with the ordinary rosin size. This property makes the use of such a type of emulsion in paper for food containers and greasy articles very valuable.

When the plant aforesaid was using ordinary rosin size it was necessary for them to use fresh water in the beater and to dilute the stock before it went to the forming machines. As this water was pumped from artesian wells it was an item of considerable expense. With the wax composition the plant could be worked in a closed system, that is, the water ture of wax, water and an emulsifying agent produces what may be termed a pre-set wax dispersion. Instead of forming an emulsion of wax by means of an emulsifying substance such as soap, adding this emulsion to the pulp in the beater, and then introducing a precipitant, I prefer to accomplish a part at least of the precipitation in advance of introduction of the wax dispersion or emulsion into the paper pulp stock. By employing such a preset or partially pre-set wax dispersion composition, preferably containing paraflin wax as the principal waxy component, I am enabled to produce a composition having the novel property of being absorbable by paper pulp stock in large proportion, that is, the major proportion of the wax is readily taken up by the pulp, with or without the addition of additional precipitant, and the minor proportion of said dispersion composition, usually representing only from 10 to 20 per cent of the entire wax, being capable of passing through the screen, felt or other web (upon which the pulp is formed into a sheet) without fouling and obstructing said web. In this respect I believe that I have obtained a wax dispersion composition possessing qualities of great importance in the manufacture of water resisting paper, pressboard, and the like.

As indicated by the foregoing the water resistant paper is prepared by adding the wax dispersion composition to pulp at any stock may be added. Preferably as in-v dicated, the proportion of wax in the finished paper may be from 1 to 2 per cent, to secure a considerable degree of water resistance and larger proportions of wax, such as 4 or 5 per cent, or, in some cases, even higher proportions, may be present. After the dispersion has been added,"followed, if desired, by a precipitant such as alum, the pulp may in due course be formed into sheets, either continuous or discontinuous, or, the pulp may be shaped in any suitablemanner. The usual paper making machines, such as the cylin der machine and the Fourdrinier machine, may be employed, thus forming a layer of the paper pulp and wax water-resistant paperproduct.

composition on a felt or wire support,as

size may be introduced into the charge in the beater engine and a composite efi'ect obtained by the presence in the paper of the waxy material and the rosin size. When the latter is used, it is essential to add to the pulp some substance such as alum, and the like, which will cause the rosin size to precipitate among the fibres. In such a case, therefore, I incorporate the pre-set wax dispersion composition and rosin size with the paper pulp. In the finished paper there may be present from, say, 1 to 3 per cent, of wax, and a like amount of rosin size material. Paper of this character not only is notably water resistant in the sense the term is employed in the case of papers of this general character, but also it has the property of exhibiting a considerable resistance to the action of grease and hence may be termed a grease-resistant and A moderately heavy paper or light board made in this manner may be employed to advantage in the production of containers for greasy foods.

On the other hand there are numerous applications of paper products treated only with the pre-set wax dispersion composition and entirely free from rosin, Which exhibit an unexpected strength and which have adesirable crackle, such paper products falling within the purview of my invention. I consider the preferred embodiment of my invention a water-resistant paper (which includes also pressboard, and the like) containing not to exceed about 5 per cent of paraffin wax, conferring such properties as have been noted above. I also include as a preferred embodiment a paper which is free, or substantially free from rosin size, yet has not only many characteristics engendered in paper by rosin size, but in addition has greater water resistance than Qwould be conferred upon paper sized with a corresponding amount of rosin size only.

It should be understood that pressboard, pulp board, and the like may not possess or be required to possess the crackle or rattle qualit noted as'a feature of the preferred embo iment in paper proper.

In applicants copending case No. 175,428, filed March 14, 1927, the grease proof paper is claimed and in copending case No. 175,440, filed March 14, 1927, there is claimed a waterresistant pa er.

Wliat Ihc aim is f 1. n t e process 0 makingpaper ul board and the like, the step which com pi ise s adding to paper pulp in the beater a quantity of at least partially pro-set wax dispersion composition to yield notto exceed about 5% of wax in the finished paper.

2. In the process of making paper manufactures, the step which comprises adding to paper pulp a wax dispersion composition which 1s at least partially pre-set.

3. In the process of making paper manufactures, the step which comprises adding to paper pulp a quantity of at least partially pre-set wax dispersion composition suflicient in amount to yield a paper having desirable crackle properties.

4. In the process of making paper manufactures, the step which comprises adding to paper pulp a wax-sodium silicate emulsion at least partially pre-set by a precipitant.

5. In the process of making paper manucomposition at least partially pre-set and having a pH value of from 7.0 to 7.3.

6. In the process of making paper manufactures, the step which. comprises adding to paper pulp having a pH value of 4.5 to 7, a wax dispersion composition which is at least partially pre-set and has a pH value of from 7 to 7.3.

7. In the process of making paper manufactures, the step which comprises adding to paper pulp having a pH value of 5.0 to 6.5, a wax dispersion composition which is at least partially pre-set. U

8. In the process of making paper manufactures, the step which comprises adding a wax dispersion composition which is at least partially pre-set and which also contains rosin, in amount sufficient to yield a finished paper having substantially grease proof properties. i

9. In the process of making paper manufactures wherein make-up chests, heaters, and forming machines are used, the steps which include draining water from the forming machines, returning the greater part of said water to the make-up chests and beaters for re-use therein, and adding thereto a substantially neutral wax dispersion composi- I tion which is at least partially pre-set.

,10. In the process of making paper manufactures, the step which comprises adding to paper pulp a wax dispersion composition which is at least partially pre-set, said composition containing a protective colloid.

11. In the process of making paper manu which is taken up by the pulp fibers, but in which any wax that is not retained on the fibers does not adhere to felts or wires of paper machines and forming machines, so that the formation of wax spots in the paper is substantially eliminated.

14. In the process of making papermanufactures, the step which comprises adding to paper pulp a non-fouling mineral wax composition which is taken up by the pulp fibers, but in which any mineral Wax that is not retained on the fibers does not adhere to felts or wires of paper machines and forming machines, so that the formation of wax spots in the paper is substantially eliminated.

15. In the process of making paper manufactures, the step which comprises adding to paper pulp a non-fouling paraffin wax emulsion, the particles of the wax being of such size that fouling does not occur under usual conditions prevailing on paper making machines.

16. In the art of paper making, the step which comprises incorporating an encysted Water-proofing agent With wet paper pulp and sheeting the pulp on a filter-web without clogging the web with said agent.

17. A. process as set forth in claim 16 in which the water-proofing agent is mineral wax.

paper pulp a composition of wax emulsified in a medium containing an emulslfylng agent under condltions to yield a non-fouling wax composition, and sheeting the pulp.

19. In the art of making paper, the steps which comprise adding to fibrous pulp, a non-fouling wax composition, and sheeting the pulp.

20. In the art of making paper, the steps which comprise adding to fibrous pulp, a wax dispersion, the particles of wax being present under conditions such that fouling does not occur under the usual conditions prevailing on paper-making machines, and sheeting the pulp.

GEORGE JAMES MANSON.

18. In the process of making paper manu- 'factures, the step which comprises adding to 

